The art of printing images with micro-fluid technology is relatively well known. A permanent or semi-permanent ejection head has access to a local or remote supply of fluid. The fluid ejects from an ejection zone to a print media in a pattern of pixels corresponding to images being printed. According to application, the fluid has dye or pigment based ink. Dye ink is typically cheap and has a broad color gamut. Pigmented ink is generally more expensive, but has a longer archival print life and higher color stability. Over time, technology has improved the color gamut of pigmented ink such that users are no longer required to choose between the broad colors available with dye ink in lieu of the improved permanence of pigmented ink.
Far from offering a printing panacea, pigmented ink is known to have layers of differing concentrations. Sediments in a container settle downward over time leaving rich concentrations near a bottom, while leaner concentrations are left near a top. As a function of height in a container above a floor, FIG. 1A details how gravity turns an initial concentration 10 of a relatively uniform or homogeneous mixture of pigmented ink into a heavily layered mixture 12 upon the passage of time. With reference also to FIG. 1B, the carbon black concentration of pigment is predicted fairly accurately by applying either the Mason/Weaver equation to particle sedimentation or a numerical analysis using finite element modeling. In either, the highest percentages of carbon black appear in the lowest heights 14 of a fluid after only a few weeks. As concentration varies relative to particle size, particle density, and fluid density and viscosity of the ink, typical pigmented inks settle into a lowest layer 16 of very high pigment concentration near the floor of the container in a height of about 2-5 mm. Above this layer, the ink settles into nominal-like concentration 18. In a top layer 20, the ink has low pigment concentration and grows deeper in the container over time.
When printing, ink drawn from a floor of a settled container leads first to excessively densely printed colors and later to excessively lightly printed colors. The variations yield unacceptable visible defects. The former can also lead to clogging of ejection head nozzles as the largest particles accumulate together in micron-sized channels having fastidious fluid flow standards.
To overcome these problems, a number of solutions have been offered. Yet, none provide economic advantage or acceptable relief across all facets of design, manufacturing and use. For example, containers are known with mechanical stir bars or other agitating members that roil ink and mix sediments before and during use. While nominally effective, the approach causes expensive/complex manufacturing and necessitates motive force during use to set the agitating bodies into motion. In other designs, ink containers have fluid exit ports raised to a height measurably higher than a floor of the container. While such avoids supplying ink to an imaging device having too dense a concentration, it prevents full use of a container's contents as appreciable amounts of ink rest below the exit port on the lowermost surfaces of the container. Still other designs contemplate both mechanical agitating members and raised exit ports. This only compounds the problems of individual designs.
Accordingly, a need exists in the art to deliver imaging devices an entirety of pigmented ink in a container. The need extends not only to an economical solution but to delivering ink in such a manner that the concentration has uniform properties over the life of the container, independent of usage rate, temperature or other imaging device conditions. Additional benefits and alternatives are also sought when devising solutions.